test: streamline examples with quit texts

Improve some examples to provide visual feedback, i.e. for the button
exmample, with fixes to make them compilable with the `Scrollable`
element changes.

examples/elements/scrollable.zig

@@ -6,7 +6,33 @@ const App = zterm.App(union(enum) {});
 
 const log = std.log.scoped(.default);
 
-pub const HelloWorldText = packed struct {
+const QuitText = struct {
+    const text = "Press ctrl+c to quit.";
+
+    pub fn element(this: *@This()) App.Element {
+        return .{ .ptr = this, .vtable = &.{ .content = content } };
+    }
+
+    pub fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Size) !void {
+        _ = ctx;
+        std.debug.assert(cells.len == @as(usize, size.cols) * @as(usize, size.rows));
+
+        const row = 2;
+        const col = size.cols / 2 -| (text.len / 2);
+        const anchor = (row * size.cols) + col;
+
+        for (text, 0..) |cp, idx| {
+            cells[anchor + idx].style.fg = .white;
+            cells[anchor + idx].style.bg = .black;
+            cells[anchor + idx].cp = cp;
+
+            // NOTE: do not write over the contents of this `Container`'s `Size`
+            if (anchor + idx == cells.len - 1) break;
+        }
+    }
+};
+
+const HelloWorldText = packed struct {
     const text = "Hello World";
 
     pub fn element(this: *@This()) App.Element {
@@ -52,6 +78,8 @@ pub fn main() !void {
     var element_wrapper: HelloWorldText = .{};
     const element = element_wrapper.element();
 
+    var quit_text: QuitText = .{};
+
     var top_box = try App.Container.init(allocator, .{
         .rectangle = .{ .fill = .blue },
         .layout = .{
@@ -59,7 +87,6 @@ pub fn main() !void {
             .direction = .vertical,
             .padding = .vertical(1),
         },
-        .min_size = .{ .rows = 50 },
     }, .{});
     try top_box.append(try App.Container.init(allocator, .{
         .rectangle = .{ .fill = .light_green },
@@ -85,7 +112,6 @@ pub fn main() !void {
             .direction = .vertical,
             .padding = .vertical(1),
         },
-        .min_size = .{ .rows = 30 },
     }, .{});
     try bottom_box.append(try App.Container.init(allocator, .{
         .rectangle = .{ .fill = .grey },
@@ -105,17 +131,17 @@ pub fn main() !void {
                 .enabled = true,
                 .line = .double,
             },
-            .padding = .all(5),
+            .padding = .{ .top = 5, .bottom = 3, .left = 3, .right = 3 },
             .direction = .vertical,
         },
-    }, .{});
+    }, quit_text.element());
     defer container.deinit();
 
     // place empty container containing the element of the scrollable Container.
-    var scrollable_top: App.Scrollable = .init(top_box);
+    var scrollable_top: App.Scrollable = .init(top_box, .{ .rows = 50 });
     try container.append(try App.Container.init(allocator, .{}, scrollable_top.element()));
 
-    var scrollable_bottom: App.Scrollable = .init(bottom_box);
+    var scrollable_bottom: App.Scrollable = .init(bottom_box, .{ .rows = 30 });
     try container.append(try App.Container.init(allocator, .{}, scrollable_bottom.element()));
 
     try app.start();